Age extracted from birth date always off by inconsistent amount

Question

I'm using the following code to convert a user-supplied birthdate to its equivalent years from the current date. The output is always off by an inconsistent amount in years and very large numbers in days and months.

NSDateFormatter *tempFormatter = [[NSDateFormatter alloc] init];
[tempFormatter setDateFormat:@"yyyy-mm-dd hh:mm:ss"];
NSDate *birthDate = [tempFormatter dateFromString:[NSString stringWithFormat:@"%@-%@-%@ 01:00:00",self.birthYear.text,self.birthMonth.text,self.birthDay.text]];

NSDate* now = [NSDate date];
NSDateComponents* ageComponents = [[NSCalendar currentCalendar]
                                   components:NSYearCalendarUnit
                                   fromDate:birthDate
                                   toDate:now
                                   options:0];
NSInteger years = [ageComponents year];
NSInteger days = [ageComponents day];
NSInteger months = [ageComponents month];
NSLog(@"Years: %ld, Days: %ld, Months: %ld",years,days, months);

What gets outputted when I input "06-16-1986" is the following

Years: 28, Days: 9223372036854775807, Months: 9223372036854775807

The year is off by 1 and the months and days are producing extremely large numbers. I get the same issue using various dates. For example, "12-07-1989" produces

Years: 25, Days: 9223372036854775807, Months: 9223372036854775807

What am I doing wrong here?

Answer 1

the problem is in this line

NSDateComponents* ageComponents = [[NSCalendar currentCalendar]
                                   components:NSYearCalendarUnit
                                   fromDate:birthDate
                                   toDate:now
                                   options:0];

if you want month & days to be calculated you need to include that in the components like this

NSDateComponents* ageComponents = [[NSCalendar currentCalendar]
                                       components:( NSYearCalendarUnit | NSDayCalendarUnit | NSMonthCalendarUnit) 
                                       fromDate:birthDate
                                       toDate:now
                                       options:0];

also your format is wrong for month string

[tempFormatter setDateFormat:@"yyyy-mm-dd hh:mm:ss"];

should be corrected as

[tempFormatter setDateFormat:@"yyyy-MM-dd hh:mm:ss"];

now you will get correct date.

explanation. as mentioned on apple documentation these are 1-based. so incase you dont provide a value it will put 1 as default. so earlier your month format was "mm" and it was not correctly setting a month for the birthday hence it was 1986-01-16 so now its 2014-04-01 (in singapore). So you get 28 years which is correct.